This application claims the benefit of Korean Application No. 99-48585, filed Nov. 4, 1999, in the Korean Patent Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to the field of data reproduction, and more particularly, to a data reproduction apparatus and method with optimum performance by adjusting filter coefficients for an equalizer to minimize a level error in detecting data.
2. Description of the Related Art
As a technique for increasing recording density by signal processing without changing the characteristics of a conventional recording/reproducing apparatus, partial response maximum likelihood (PRML) related technique, including Viterbi decoding, has advanced.
Viterbi decoders have a predetermined reference level for use in detecting an error value of data. To match the level of input data of a Viterbi decoder to the predetermined reference level, filter tap coefficients of an equalizer connected in front of the Viterbi detector are adjusted to output data whose level matches the reference level of the Viterbi detector.
FIG. 1 illustrates a coefficient adaptation method of a conventional equalizer. An analog-to-digital converter (ADC) 10 samples an input radio frequency (RF) signal, and an asymmetry compensator 12 and an adder 14 correct for asymmetry or a DC offset component of the sample RF signal and provides the result to an equalizer 16. A 3T level error detector 18 detects a difference, i.e., error (ek), between a reference value and the minimum pit (or mark) level, which corresponds to 3T (where T is a pit interval) in a conventional digital versatile disc (DVD) or compact disc (CD)), output from the equalizer 16 which is constituted of a finite impulse response (FIR) filter.
If the error value detected by the 3T level error detector 18 is a positive value, a filter coefficient adjuster 20 determines that the minimum pit level is larger than the reference value. In this case, the filter coefficient adjuster 20 provides the equalizer 16 with a filter coefficient Wk+1, which is adjusted to decrement a filter coefficient Kb and increment a filter coefficient Ka, to decrease the minimum pit level output from the equalizer 16. To the contrary, if the error value detected by the 3T level error detector 18 has a negative value, the filter coefficient adjuster 20 determines that the minimum pit level is smaller than the reference value. As a result, the filter coefficient adjuster 20 provides the equalizer 16 with the filter coefficient Wk+1, which is adjusted to decrement the filter coefficient Ka and increment the filter coefficient Kb, to increase the minimum pit level output from the equalizer 16. The minimum pit level is adjusted to an appropriate level in the above manner, so that the performance of the Viterbi detector 22 is enhanced.
FIG. 2 illustrates the structure of the equalizer 16. In FIGS. 1 and 2, xk indicates data input to the equalizer 16, yk indicates data output from the equalizer 16, and Wk+1 indicates the filter coefficient for the equalizer 16 after coefficient adaptation. Reference numerals 30, 32, 34, 36, 38, 40, 42 and 44 denote delays, reference numerals 46, 48 and 50 denote coefficient multipliers, and reference numeral 52 denotes an adder.
With the structure of the conventional equalizer, detection of the minimum pit level is difficult and level error detection is restricted because only a middle level of the minimum pit is used. Thus, it is difficult to expect a great improvement in reproduction performance. In addition, even though defocusing occurs, the coefficient adaptation in the conventional equalizer ensures the improvement of reproduction performance, by adjusting filter coefficients. However, the conventional equalizer cannot be adopted when the coefficients of the equalizer asymmetrically vary due to tangential tilting.
To solve the above problems, it is an object of the present invention to provide a data reproduction apparatus and method with improved performance, which can be adopted for a recording medium such as an optical disk.
It is a second object of the present invention to provide a data reproduction apparatus and method with improved performance, which selects filter coefficients for an equalizer such that a level error is minimized.
It is a third object of the present invention to provide a data reproduction apparatus and method with improved performance, which adaptively selects filter coefficients for an equalizer such that a level error is minimized.
If is a fourth object of the present invention to provide a data reproduction apparatus and method which monitors the servo status, such as the direction of tangential tilting, or defocusing status, according to variations in filter coefficients.
It is a fifth object of the present invention to provide a data reproduction apparatus and method with improved performance, which adaptively selects filter coefficients for an equalizer, in consideration of the servo status, such as the direction of tangential tilting, or defocusing status, according to variations in filter coefficients.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and, in part, will be obvious from the description, or may be learned by practice of the invention.
According to an aspect of the present invention, there is provided a data reproduction apparatus including a data detector which detects data based on partial response maximum likelihood (PRML). The apparatus includes an equalizer comprising a digital filter. A level error detector extracts a level of the output value of the equalizer based on a reference level set in the data detector and detects a level error between the level of the output value and a predetermined reference value. A coefficient bank stores filter coefficients of the equalizer and a coefficient selector selects the filter coefficients of the equalizer from the coefficient bank such that the level error is minimized.
In another embodiment, the present invention provides a data reproduction apparatus including a data detector which detects data based on partial response maximum likelihood (PRML). The apparatus includes an equalizer comprising a digital filter. A level error detector extracts a level of the output value of the equalizer based on a reference level set in the data detector and detects a level error between the level of the output value and a predetermined reference value. A coefficient adapter adapts filter coefficients of the equalizer such that a difference between the level error and a target level error is minimized.
Preferably, the data reproduction apparatus includes a defocus/tilt detector which detects the servo status by monitoring variations of the adaptive filter coefficients of the equalizer.
According to another aspect of the present invention, there is provided a data reproduction method which improves the performance of a data detector which detects data based on partial response maximum likelihood (PRML) by adjusting filter coefficients of an equalizer comprising a digital filter, connected before the data detector. The method includes extracting a level of the output data of the equalizer based on a reference level set in the data detector, and detecting a level error between the level of the output data and a predetermined reference value; and adjusting the filter coefficients of the equalizer such that the level error is minimized.